Method of and system for tracing monochromatically contrasting pattern

ABSTRACT

A method of and a system for tracing a monochromatically contrasting pattern on a uniplanar surface, in which signals indicative of a detected image of the pattern are produced by photoelectric transducer elements arranged in a two-dimensional or linear matrix array and signals indicative of a suitable number of modified reference areas displaced a predetermined distance from a prescribed basic reference area formed on a plane parallel with the uniplanar surface are produced from memory units having the modified reference areas registered therein, whereupon signals indicative of areas over which the detected image sensing zone is overlapped by the modified reference areas are produced to determine the direction in which the matrix array is to be moved with respect to the pattern on the uniplanar surface.

FIELD OF THE INVENTION

The present invention relates to a method of and a system for tracing amonochromatically contrasting geometrical or graphic pattern on auniplanar surface such as a sheet of drawing carrying a linear orcurvilinear line.

BACKGROUND OF THE INVENTION

An example of prior-art pattern tracing systems of the nature abovementioned is disclosed in U.S. Pat. No. 3,423,589 showing aphotoelectric pattern-contour tracing system in which a sensing headhaving two discrete photocells is rotatable about its center axis and ismovable over and along the pattern contour to be traced. The sensinghead is positioned with respect to the pattern contour in such a mannerthat the two photocells are spaced apart in a direction perpendicular innon-intersecting relationship to the pattern contour. When the sensinghead assumes a position having the photocells located symmetrically withrespect to the width of the pattern contour, viz., when the center lineof the spacing between the photocells is located accurately above thelongitudinal center line of the pattern contour, the photocells aresubjected to light of equal intensities so that the currentsrespectively produced by the photocells are equal in magnitude to eachother. When the sensing head is deviated from the correct position overthe pattern contour, the two photocells sense light of differentintensities and thus produce currents with different magnitudes. Thepath along which the sensing head is to travel is adjusted upondetection of such a difference between the magnitudes of the currentsrespectively produced by the two photocells.

Since the adjustment of the path along which the sensing head is toadvance is thus made through detection of the currents actually producedby the photocells moved with the sensing head, the sensing head must bemoved and turned in various directions before a correct path isdetermined. For this reason, the sensing head must be equipped orassociated with a disproportionately large number of mechanical membersand structures which are subject to erroneous motion and failure duringoperation and which will add to the measurements, weight and productionand mainterance costs of the tracing system as a whole. Because,furthermore, of the fact that the sensing head essentially consists ofonly two photocells which are juxtaposed in close proximity to eachother and which are to be moved along the pattern to be traced, thesensing head can not be satisfactorily sensitive to acute angles and tolines extending in close proximity to each other.

Another example of known pattern tracing systems is taught in Japanesepatent Publication No. 49-42803 showing a photoelectric pattern tracingsystem using a two-dimensional matrix array consisting of a number ofphotoelectric transducer elements arranged on xy-coordinates. The matrixarray is positioned over the pattern to be traced and produces binarysignals from those transducer elements which are located above a portionof the pattern. When the matrix array assumes a certain position overthe portion of the pattern, one of the transducer elements producesbinary signals indicating the location of a specific point of theportion of the pattern in terms of the xy-coordinates of the matrixarray and another one of the transducer element produces binary signalsindicative of the location of the leading end of the portion of thepattern in terms of the xy-coordinates. The matrix array is thus movedfrom the position indicated by the binary signals proudced by the formertransducer element to the position indicated by the binary signalsproduced by the latter transducer element. Only the direction in whichthe portion of the pattern to be traced is detected by the matrix array,which is therefore not responsive to the width of the pattern and whichis accordingly not capable of recognizing acute angles and lines whichare close to each other.

The present invention contemplates elimination of these and otherdrawbacks inherent in prior-art pattern tracing systems of the describedgeneral natures.

SUMMARY OF THE INVENTION

In accordance with one outstanding aspect of the present invention,there is provided a method of tracing a monochromatically contrastingpattern on a uniplanar surface, comprising photoelectrically scanning atleast a portion of the pattern of the uniplanar surface for producingsignals forming on a plane substantially parallel with the uniplanarsurface a detected image sensing zone substantially similar inconfiguration to the portion of the pattern on the uniplanar surface,registering pieces of information representative of a predeterminednumber of modified reference areas each displaced a predetermineddistance in a predetermined direction from a prescribed basic area onthe aforesaid plane, sampling the pieces of information for deliveringsignals representative of each of the individual modified referenceareas, producing in responsive to the signals representative of thedetected image sensing zone and the signals representative of each ofthe modified reference areas a signal representative of the overlap areaover which the detected image sensing zone is overlapped by each of themodified reference area, selecting from among the individual signalsrespectively representative of the overlap areas between the detectedimage sensing zone and the modified reference areas a signalrepresentative of an overlap area satisfying predetermined conditions,producing a control signal representative of the predetermined directionallocated to the modified reference area corresponding the signalselected, and photoelectrically scanning another portion of the patternon the uniplanar surface depending upon the control signal.

In accordance with another outstanding aspect of the present invention,there is provided a photoelectric pattern tracing system for tracing amonochromatically contrasting pattern on a uniplanar surface, comprisingan image sensing unit which is movable on a plane substantially parallelwith the uniplanar surface and which is photoelectrically responsive tothe pattern on the uniplanar surface, a predetermined number of memoryunits each having stored therein pieces of information representative ofa modified reference area displaced a predetermined distance in apredetermined direction from a prescribed basic reference area on theaforesaid plane, image readout means operative to electrically scan theimage sensing unit for causing the image sensing unit to deliver signalsin response to at least a portion of the pattern, the signals forming onthe above mentioned plane a detected image sensing zone substantiallysimilar in configuration to the aforesaid portion of the pattern, memoryreadout means operative to sample the pieces of information stored ineach of the memory units for causing the individual memory units todeliver signals representative of the modified reference areasrespectively allocated to the memory units, an overlap area monitorcircuit responsive to the signals delivered from the image sensing unitand the memory units and operative to produce a signal representative ofthe overlap area over which the basic reference area represented by thesignals delivered from the image sensing unit is overlapped by themodified reference area represented by the signals delivered from eachof the memory units, computing means responsive to the signal from theoverlap area monitor circuit and operative to select from among thesignals produced by the overlap area monitor circuit a signalrepresentative of an overlap area satisfying predetermined conditionsand to produce an output signal representative of the predetermineddirection allocated to the memory unit from which the signals resultingin the signal selected by the computing means are delivered, and drivemeans responsive to the output signal from the computing means andoperative to drive the image sensing unit to move a predetermineddistance on the aforesaid plane in the direction represented by theoutput signal from the computing means.

In accordance with still another outstanding aspect of the presentinvention, there is provided a combination of the new photoelectricpattern tracing system and a machine tool such as an oxyacetylene torch.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of a photoelectric pattern tracing systemaccording to the present invention will be more clearly appreciated fromthe following description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a schematic perspective view showing, largely in a blockdiagram, a preferred embodiment of the pattern tracing system accordingto the present invention;

FIG. 2 is a schematic plan view showing, partly in a block diagram, theimage sensing unit and the image and memory readout means forming partof the embodiment shown in FIG. 1;

FIG. 3 is a plan view showing, to an enlarged scale, thearea-configuration matrix array of photoelectric transducer elementsforming part of the image sensing unit in the arrangement illustrated inFIG. 2;

FIG. 4 is a diagram showing the principles on the basis of which thebasic and modified reference areas used as reference indexes in theembodiment of FIG. 1 are to be formulated in regard to the detectedimage sensing zone representative of a portion of the pattern to betraced;

FIG. 5 is a block diagram showing preferred examples of the circuitarrangement of the memory and overlap area monitor circuits forming partof the embodiment illustrated in FIG. 1;

FIG. 6 is a flowchart representative of the various steps to be taken inthe central processing unit in the embodiment of FIG. 1;

FIG. 7 is a schematic view showing the arrangement in which anotherpreferred embodiment of the present invention is to operate;

FIG. 8 is a graphic representation of the detected image sensing zoneformed by a linear-configuration rotary matrix array in the arrangementillustrated in FIG. 7;

FIG. 9 is a graphic representation of the modified reference areas to beregistered in the embodiment of FIG. 7; and

FIG. 10 is a graphic representation of the area over which the detectedimage sensing zone indicated in FIG. 8 is overlapped by one of themodified reference areas shown in FIG. 9.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first preferred embodiment of the photoelectric pattern tracing systemaccording to the present invention will be hereinafter described indetail with reference to the accompanying drawings, particularly FIGS. 1to 6 thereof.

Referring first to FIG. 1 of the drawings, the photoelectric patterntracing system according to the present invention is used for thepurpose of tracing a monochromatically contrasting geometric orgraphical pattern carried on a uniplanar surface of a suitable recordingmedium which is shown, by way of example, to be in the form of a sheetof drawing 10 carrying a dark, curvilinear pattern 12 on its brightfront face. In FIG. 1, furthermore, the photoelectric pattern tracingsystem proposed by the present invention is assumed, by way of example,to be used in combination with an oxyacetylene cutting torch 14 formaking in a ferrous or wrought-iron sheet 16 a curvilinear cut 18 whichis identical in configuration with the curvilinear pattern 12 on thedrawing 10. The cutting torch 14 is coupled to a gas hose 20 leadingfrom a suitable supply source (not shown) of oxyacetylene gas underpressure. If desired, the single cutting torch 14 as shown may besubstituted by a set of oxyacetylene cutting torches arranged inparallel with one another on a common torch carrier (not shown).

In FIG. 1, the photoelectric pattern tracing system embodying thepresent invention is shown comprising a photoelectric image sensing unit22 which is movable in two directions perpendicular to each other on acommon plane parallel with the front face of the drawing 10. In thearrangement herein shown, the drawing 10 is assumed to be positioned ona horizontal plane with its front face directed upwardly so that thephotoelectric image sensing unit 22 is movable over the front face ofthe drawing 20 in two horizontal directions perpendicular to each otheras indicated by arrows x and y. The cutting torch 14 or the abovementioned common torch carrier having a plurality of cutting torchessupported thereon is mechanically connected to the sensing unit 22 bymeans of a suitable coupling mechanism which is shown including a singleconnecting bar 24 connected at one end to the sensing unit 22 and at theother to the cutting torch 14. The cutting torch 14 or the common torchcarrier is, thus, also movable in two horizontal directionsperpendicular to each other over the front or upper face of theworkpiece 16 which is also assumed to be positioned horizontally.

Turning to FIG. 2 of the drawings, the photoelectric image sensing unit22 comprises a two-dimensional image sensing matrix array 26 consistingof a predetermined number of separate and discrete photoelectrictransducer elements 28 which are arranged in predetermined numbers ofrows and columns on a common plane parallel with the plane on which thesensing unit 22 is movable. The image sensing matrix array 26 iselectrically connected to first and second or X-axis and Y-axis shiftregisters 30 and 32 which constitute image readout means in the tracingsystem according to the present invention. The X-axis shift register 30is adapted to sequentially sample the individual photoelectrictransducer elements of each row at a predetermined frequency in responseto a series of actuating signals successively supplied to the shiftregister 30. On the other hand, the Y-axis shift register 32 is adaptedto sequentially select the rows of the transducer elements 28 inresponse to actuating signals supplied in succession from the X-axisshift register 30 upon completion of the sampling of the individual rowsof the transducer elements 28 by the X-axis shift register 30. Each ofthe X-axis and Y-axis shift registers 30 and 32 to achieve thesefunctions may be constituted by an ordinary digital shift registerusing, for example, a series of set-reset flipflops.

In FIG. 3, the photoelectric transducer elements 28 constructing thetwo-dimensional image sensing matrix array 26 are shown arranged in theform of 50×50 matrix. A total of 2,500 transducer elements 28 thusarranged are, by way of example, assumed to be mounted on asquare-shaped silicon substrate measuring 1.8 cm in both length andbreadth and respectively constituted by diffused p-n junctionphotodiodes. When each of the photoelectric transducer elements 28 iselectrically energized in the presence of light falling on thetransducer element, the transducer element 28 produces an electricoutput signal which is largely proportional in magnitude to theintensity of the light incident on the transducer element as is wellknown in the art. Each of the transducer elements 28 forms part of anelectric network adapted to produce a binary signal depending upon themagnitude of the analog signal produced by the transducer element but isherein assumed for brevity of description to be operative to produce initself a logic "1" output signal in response to the light reflected froma dark surface and a logic "0" output signal in response to the lightreflected from a bright surface. It therefore follows that, when theimage sensing matrix array 26 is positioned above a portion of thecurvilinear pattern 12 on the front face of the drawing 10 and providedall the photoelectric transducer elements 28 of the matrix array 26 thuspositioned are energized concurrently, each of the transducer elements28 located above the portion of the curvilinear pattern 12 is actuatedto produce a logic "1" output signal and each of the remainingtransducer elements 28 of the matrix array 26 produces a logic "0"output signal. In FIG. 3, those transducer elements 28 which are locatedabove the particular portion of the curvilinear pattern 12 and which arethus producing logic "1" output signals are indicated by sections eachmarked with a dot. The photoelectric transducer elements 28 representedby the dotted sections form a detected image sensing zone M responsiveto the image of the above mentioned portion of the curvilinear pattern12 on the drawing 10 as schematically indicated in FIG. 4.

Reverting to FIGS. 1 and 2, the X-axis shift register 30 is connected bya line 34 to a clock generator module 36 (shown in block form in FIG. 1)and is cyclically actuated by a series of clock pulses supplied at apredetermined frequency from the clock generator module 36. In responseto each of the clock pulses thus supplied in succession from the clockgenerator module 36, the X-axis shift register 30 is actuated to sampleeach of the photoelectric transducer elements 28 of the row selected bythe Y-axis shift register 32. The individual photoelectric transducerelements 28 of each row are thus sequentially scanned by the X-axisshift register 30 and produce logic "1" or "0" output signals as clockpulses are supplied successively from the clock generator module 36. Thelogic "1" or "0" output signals thus delivered from the image sensingmatrix array 26 are successively supplied through a line 40 to anoverlap area monitor circuit 42 the functions of which will be describedlater. Upon completion of the sampling of the photoelectric transducerelements 28 of each row, an end-of-scan signal is supplied from theX-axis shift register 30 to the Y-axis shift register 32 via a line 38interconnecting the two shift registers 30 and 32 and actuates theY-axis shift register 32 to select the next row of photoelectrictransducer elements 28 for enabling the X-axis shift register 30 tosample the photoelectric transducer elements 28 of the row newlyselected. When the last one of the photoelectric transducer elements 28of the last row is accessed by the X-axis shift register 30, anend-of-frame signal is delivered from the Y-axis shift register 32 andis fed through a line 44 to the above mentioned overlap area monitorcircuit 42 and further to a central processing unit (CPU) 46.

Referring again to FIG. 3 of the drawings, the generally circular,hatched area defined by thick, stepped boundary lines indicates a basicreference area which is representative of the area which is to be cutout in the workpiece 16 (FIG. 1) by the jet flame produced by thecutting torch 14 or each of the previously mentioned cutting torchescarried by a common torch carrier when the cutting torch is held at restabove the workpiece. In the present invention, there is furtherintroduced the concept and term of "modified reference area". A modifiedreference area herein referred to is defined as the area which isimaginarily obtained on the image sensing matrix array 26 when the abovementioned basic reference area No is moved a predetermined distance dfrom its original position on the matrix array 26 in one of fourpredetermined directions angled to each other on a common plane parallelwith the plane on which the photoelectric transducer elements 28 arearranged. In the embodiment of the present invention, four modifiedreference areas Na, Nb, Nc and Nd are considered, which are to beobtained on the image sensing matrix array 26 when the basic referencearea N is moved the predetermined distance d from its original positionin first, second, third and fourth directions which are successivelyangled at 90 degrees to each other as indicated by a, b, c and d,respectively, in FIG. 4, viz., forwardly, rearwardly, rightwardly andleftwardly when viewed in FIG. 4. In FIG. 4, the amount of displacementof each of the modified reference areas Na to Nd from the basicreference area N is shown exagerated but is preferably such that issubstantially equal to the measurement of each of the transducerelements 28.

The first to fourth modified reference areas Na, Nb, Nc and Nd areregistered in a memory circuit 48 (FIG. 1) which is connected by anaddress bus 50 to a memory address signal generator 52 (FIG. 2) whichconstitutes memory readout means in the pattern tracing system accordingto the present invention and which may be incorporated into the imagesensing unit 22. The memory address signal generator 52 in turn isconnected by a bus 54 to the X-axis shift register 30 and by a bus 56 tothe Y-axis shift register 32 as shown in FIG. 2. As the rows of thephotoelectric transducer elements 28 are successively selected by theY-axis shift register 32 and the individual photoelectric transducerelements 28 of the selected row are sampled by the X-axis shift register30, a signal representative of the location in the selected row of thephotoelectric transducer element 28 being sampled and a signalrepresentative of the selected row of the photoelectric transducerelements 28 are fed from the X-axis and Y-axis shift registers 30 and 32to the memory address signal generator 52 through the buses 54 and 56,respectively, and causes the signal generator 52 to produce an addresssignal respresentative of the coordinate location in the matrix array 26of the particular photoelectric transducer element 28 being sampled bythe X-axis shift register 30. A series of address signals are thussuccessively supplied from the addressing signal generator 52 to thememory circuit 48 through the memory bus 50 and actuate the memorycircuit 48 to read out the above described first to fourth modifiedreference areas Na, Nb, Nc and Nd synchronously as the photoelectrictransducer elements 28 of the image sensing matrix array 26 are sampledsequentially by the X-axis shift register 30. The memory circuit 48 hasoutput terminals connected by lines 58 to the overlap area monitorcircuit 42.

Referring to FIG. 5 of the drawings, the memory circuit 48 comprisesfour, first to fourth, memory units 48a, 48b, 48c and 48 d having inputports connected by the address bus 50 to the memory address signalgenerator 52 (FIG. 2). The first to fourth memory units 48a, 48b, 48cand 48d have registered therein the previously mentioned first to fourthmodified reference areas Na, Nb, Nc and Nd, respectively, and aretriggered concurrently each time an address signal is supplied from thememory address signal generator 52 through the address bus 50. Each ofthe memory units 48a, 48b, 48c and 48d consists of a number of memorycells respectively allocated to the individual photoelectric transducerelements 28 of the image sensing matrix array 26 and is adapted toproduce a logic "1" or "0" output signal depending upon whether thetransducer element 28 corresponding to the particular memory cellaccessed by an address signal supplied to the memory unit falls withinor outside the modified reference area registered in the memory unit. Inthe arrangement herein shown, it is assumed by way example that each ofthe memory units 48a, 48b, 48c and 48d is adapted to produce a logic "1"output signal when the transducer element 28 corresponding to theparticular memory cell sampled by an address signal supplied to thememory unit falls within the modified reference area registered in thememory. If, therefore, the transducer element 28 corresponding to thememory cell sampled by an address signal supplied to, for example, thefirst memory unit 48a falls within the first modified reference area Na,the memory unit 48a produces a logic "1" output signal. If, conversely,the transducer element 28 corresponding to the memory cell accessed bythe address signal supplied to the memory unit 48a happens to be outsidethe first modified reference area Na, then the memory unit 48a producesa logic "0" output signal. Each of the first to fourth memory units 48ato 48d is thus actuated to successively produce logic "1" and/or "0"output signals as address signals respectively representative of thecoordinate locations of the photoelectric transducer elements 28 beingsampled by the X-axis shift register 30 (FIG. 2) are fed to the memoryunit. The output signals thus produced by the four memory units 48a to48d are supplied through the lines 58 to the overlap area monitorcircuit 42.

The overlap area monitor circuit 42 is adapted to monitor the area overwhich the detected image sensing zone M shown in FIG. 3 is overlapped byeach of the first to fourth modified reference areas Na to Nd andcomprises four, first to fourth, logic "AND" gate circuits 60a, 60b, 60cand 60d each having two, first and second, input terminals. The firstinput terminals of the logic "AND" gate circuits 60a to 60d areconnected by lines 58a to 58d to the first to fourth memory units 48a to48d, respectively. The respective second input terminals of the logic"AND" gate circuits 60a to 60d are connected jointly to the line 40leading from the image sensing matrix array 26. Thus, each of the firstto fourth logic "AND" gate circuits 60a to 60d is adapted to produce alogic "1" output signal in the presence of logic "1" signals at both ofits first and second input terminals, viz., when the photoelectrictransducer element 28 being sampled by the X-axis shift register 30falls within the detected image sensing zone M and concurrently thetransducer element 28 corresponding to the memory cell accessed by anaddress signal impressed on each of the memory units 48a and 48d fallswithin the modified reference area Na, Nb, Nc or Nd registered in theparticular memory unit. The memory address signal generator 52 isarranged to produce address signals in synchronism with the individualscanning steps taken by the X-axis shift register 30 so that each of theabove described logic "AND" gate circuits 60a to 60d is operative toproduce a logic "1" output signal each time the photoelectric transducerelement 28 corresponding to the memory cell sampled by an address signalsupplied to the respectively associated one of the memory units 48a to48d falls within both the detected image sensing zone M and the modifiedreference area Na, Nb, Nc or Nd registered in the particular memoryunit.

Each of the memory units 48a to 48d constituting the memory circuit 48is preferably of a programmable nature so that the modified referencearea to be registered therein can be changed or adjusted depending uponthe desired width of the cut to be made in the workpiece and/or thewidth of the pattern to be traced. Such a memory unit may be constitutedby, for example, a programmable read only memory (PROM) or a randomaccess memory (RAM). The memory units 48a to 48d are thus shownconnected to the central processing unit 46 by a control bus 62 so thateach of the memory units can be programmed or re-programmed from thecentral processing unit 46.

The overlap area monitor circuit 42 further comprises four, first tofourth, digital counter circuits 64a, 64b, 64c and 64d having inputterminals connected to the output terminals of the first to fourth logic"AND" gate circuits 60a, 60b, 60c and 60d, respectively, and triggerterminals jointly connected to the clock generator module 36 (FIG. 1)through the line 34. The counter circuits 64a to 64d further have resetterminals jointly connected to the Y-axis shift register 32 through theend-of-frame signal line 44. Each of the counter circuits 64a to 64d isthus adapted to count the logic "1" output signals from the associated"AND" gate circuit 60a, 60b, 60c or 60d in synchronism with the clockpulses supplied to the counter circuit through the line 34. Uponcompletion of the readout of all the photoelectric transducer elements28 of the image sensing matrix array 26 (FIGS. 2 and 3), theend-of-frame signal is supplied to each of the counter circuits 64a to64d through the line 44 and causes each counter circuit to produce anoutput signal representative of the number of the counts registeredtherein. The counter circuits 64a to 64d are thereafter cleared and aremade ready for operation in the subsequent scanning cycle. Therespective output signals produced by the counter circuits 64a to 64dare fed to the central processing unit 46 through buses 66a to 66d(which are represented by a bus 66 in FIG. 1). As will be readilyunderstood, each of the output signals thus delivered from the first tofourth counter circuits 64a to 64d to the central processing unit 46 isrepresentative of the area over which the detected image sensing zone Mand each of the first to fourth modified reference areas Na to Nd,respectively, overlap each other. The central processing unit 46constitutes computing means in the pattern tracing system according tothe present invention and is basically operative to select from amongthe signals respectively delivered from the first to fourth countercircuits 64a to 64d a signal representative of an overlap areasatisfying predetermined conditions and to produce an output signalrepresentative of the direction a, b, c or d (FIG. 4) allocated to thememory unit 48a, 48b, 48c or 48d from which the signals resulting in thesignal selected by the central processing unit 46 are delivered.

In response to the output signals delivered from the overlap areamonitor circuit 42, the central processing unit 46 is caused to startoperation as indicated at 68 in the flowchart of FIG. 6 and registers ina first step 70 the pieces of information representative of the fouroverlap areas over which the detected image sensing zone M is overlappedby the first to fourth modified reference areas Na to Nd. The step 70 isfollowed by a second step 72 to check whether or not all the overlapareas registered in the first step 70 are zeros. If, in this instance,the answers in the second step 72 are all in the affirmative "YES",viz., all the modified reference areas Na, Nb, Nc and Nd are locatedoutside the detected image sensing zone M, a signal is produced in athird step 74 for interrupting the movement of the photoelectric sensingunit 22 (FIG. 1) and adjusting the position of the sensing unit 22 withrespect to the pattern 12 on the drawing 10 by, for example, humanintervention.

If, however, at least one of the answers taken in the second step 72 isin the negative "NO", viz., at least one of the overlap areas over whichthe detected image sensing zone M is overlapped by the first to fourthmodified reference areas Na to Nd is not zero, then the pieces ofinformation registered in the first step 70 are processed in a fourthstep 76 wherein the direction a, b, c or d (FIG. 4) in which thephotoelectric image sensing unit 22 (FIG. 1) was moved during theimmediately preceding cycle of operation is registered. In the fourthstep 76, the pieces of information representative of the four overlapareas are processed to determine and exclude the overlap area formed bythe modified reference area Na, Nb, Nc or Nd which corresponds to thedirection a, b, c or d registered in the step 76. The pieces ofinformation representative of the remaining three overlap areas arefurther processed in a fifth step 78 so as to determine whether or notone and only one of the three overlap areas is closer to a predeterminedvalue than the other two. If the answer in the fifth step 78 is in theaffirmative "YES" , viz., only one of the selected three overlap areasis closer to the predetermined value than the other two of the threeoverlap areas, a control signal Sx or Sy representative of the directionin which the photoelectric sensing unit 22 is to be moved over thedrawing 10 (FIG. 1) is produced in a sixth step 80. If, however, theanswer taken in the fifth step 78 is in the negative "NO", viz., thethree overlap areas selected in the fourth step 76 are equal to eachother or two of the selected three overlap areas are equal to each otherand are closer to the predetermined value than the remaining one of thethree overlap areas, a control signal Sn is produced in a seventh step82, calling for movement of the photoelectric sensing unit 22 in thesame direction as the direction in which the sensing unit 22 was causedto move during the immediately preceding cycle of operation. The controlsignal Sx or Sy produced in the sixth step 80 or the control signal Snproduced in the seventh step 82 is registered in an eighth step 84 andthrough the eighth step 84 further registered in the fourth step 76. Theeighth step 84 is followed by a ninth step 86 in which it is confirmedwhether or not the tracing operation for the drawing 10 (FIG. 1) iscomplete. If the answer in the ninth step 86 is in the affirmative"YES", an end-of-program signal appears in a tenth step 88. If, however,the answer in the ninth step 86 is in the negative "NO", viz., thetracing operation is still to go on, the central processing unit 46 iskept ready to register in the first step 70 new pieces of information tobe produced in the subsequent cycle of operation.

The control signal Sx or Sn or the control signal Sy or Sn produced inthe sixth or seventh step 80 or 82 in the central processing unit 46 isfed through a line 90 or a line 90' to an X-axis drive unit 92 or aY-axis drive unit 92', respectively, which is drivingly connected to thephotoelectric sensing unit 22 as shown schematically in FIG. 1. Inresponse to the control signal Sx, Sy or Sn, the X-axis drive unit 92 orthe Y-axis drive unit 92' is actuated to drive the photoelectric sensingunit 22 to move a predetermined unit distance in a direction indicatedby arrow x in FIG. 1, viz., rightwardly or leftwardly over the frontface of the drawing 10 or in a direction indicated by arrow y in FIG. 1,viz., forwardly or rearwardly depending upon the polarity of the controlsignal Sx, Sy or Sn supplied to the drive unit 92 or 92'. The abovementioned predetermined unit distance over which the photoelectricsensing unit 22 is to be moved each time the drive unit 92 or 92' isactuated is preferably the previously mentioned predetermined distance dwhich each of the modified reference areas Na to Nd is displaced fromthe basic reference area N in the matrix array 26 illustrated in FIGS. 3and 4. Each of the X-axis and Y-axis drive units 92 and 92' may beconstituted by a pulsed stepping motor. The predetermined value withwhich the three overlap areas selected in the fourth step 76 are to becompared in the fifth step 78 may be selected so that the overlap areaselected in the fifth step 78 has an arc portion located on or inproximity to the center line of the detected image sensing zone M shownin FIGS. 3 and 4.

A second preferred embodiment of the photoelectric pattern tracingsystem according to the present invention will be hereinafter describedwith reference to FIGS. 7 to 9 of the drawings.

While the photoelectric image sensing unit 22 of the embodiment of thetracing system hereinbefore described uses the two-dimensional orarea-configuration image sensing matrix array 26, the photoelectricimage sensing unit incorporated in the second embodiment of the presentinvention comprises a linear-configuration rotary photoelectric matrixarray 94 having a suitable number of photoelectric transducer elements96 arranged linearly on a common elongated substrate. The photoelectricmatrix array 94 is rotatable about one end thereof on a plane parallelwith the front face of a drawing (not shown) carrying a dark, uniplanarpattern on the front face. The photoelectric transducer elements 96constituting the matrix array 94 are herein assumed to be 32 in numberby way of example and are denoted by D₁, D₂, D₃, . . . D₃₂ from the axisof rotation of the matrix array 94 to the outermost end of the array 96as indicated in FIG. 7. Each of the photoelectric transducer elements 96is preferably constructed by a diffused p-n junction photodiodesimilarly to the photoelectric transducer elements 28 constituting theimage sensing matrix array 26 in the first embodiment of the presentinvention.

The length of the linear-configuration matrix array 94, viz., the radiusof rotation of the matrix array 94 about its innermost end is assumed tobe substantially equal to the radius of the previously mentioned basicreference area N in the area-configuration photoelectric matrix array 26shown in FIG. 3. When, thus, the matrix array 94 turns about theinnermost end thereof, the matrix array 94 describes a circular scanningarea as indicated by S in FIG. 7. If, therefore, the matrix array 94 isrotated about its innermost end on a plane parallel with the front faceof the drawing, those photoelectric transducer elements 96 which travelin proximity to a portion of the pattern on the front face of thedrawing will produce a logic "1" output signal in response to the lightreflected from the particular portion of the pattern and thereby form adetected image sensing zone M' within the circular scanning area S asindicated by a hatched area in FIG. 7. It will be apparent that thedetected image sensing zone M' thus formed by the linear-configurationmatrix array 94 corresponds to the previously mentioned detected imagesensing zone M formed by the area-configuration photoelectric matrixarray 26 shown in FIGS. 3 and 4.

If, thus, the linear-configuration matrix array 94 is rotated about itsinnermost end in a direction indicated by arrow e in FIG. 7 and if thephotoelectric transducer elements 96 constituting the matrix array 94are sampled at each of time intervals respectively corresponding topredetermined angular intervals of, for example, 10 degrees about theaxis of rotation of the matrix array 94, the matrix array will producelogic "1" output signals with a characteristic represented by a hatchedarea H in the graph of FIG. 8. In FIG. 8, θ₁, θ₂, . . . θ₅ represent theangles of rotation at certain angular intervals from a certain angle θ₁at which the matrix array 94 rotated from a predetermined initial lineOX in polar coordinates having an origin O at the axis of rotation ofthe matrix array 94 first responds to the pattern on the front face ofthe drawing and commences formation of the detected image sensing zoneM' as shown in FIG. 7. Thus, the hatched area H shown in FIG. 8 isrepresentative of the detected image sensing zone M' shown in FIG. 7 andwill therefore be hereinafter referred to also as detected image sensingzone.

If a circle having a radius smaller than the radius of the circularscanning area S is described about the origin O in the polar coordinatesillustrated in FIG. 7, an area N' equivalent to the previously mentionedbasic reference area N can be obtained within the scanning area S. If,in this instance, the radius of the basic reference area N' thus formedis selected to be equal to the distance between the respective centerpoints of the first transducer element D₁ and the p-th transducerelement D_(p) of the matrix array 94, the above mentioned basicreference areas N' is represented by the area R lower than line f in thegraph of FIG. 8. It therefore follows that the area over which the basicreference area N' shown in FIG. 7 is overlapped by the detected imagesensing zone M' is represented by that portion Hf of the detected imagesensing zone H which is lower than the line f in the graph of FIG. 8.Thus, the overlap area between the basic reference area N' and thedetected image sensing zone M' shown in FIG. 7 is represented by theportion Hf of the detected image sensing zone H in the graph of FIG. 8and can accordingly be digitally detected by counting the number of thelogic "1" signals represented by the particular portion Hf, viz., thenumber of the logic "1" output signals produced by the first to p-thphotoelectric transducer elements D₁ to D_(p) of the matrix array 94.

If, on the other hand, the basic reference area N' as above defined isdisplaced a predetermined distance from its original position in fourpredetermined directions which are successively angled at 90 degrees toeach other, viz., forwardly, rearwardly, rightwardly and leftwardly inFIG. 7, the resulting four areas are respectively equivalent to thepreviously mentioned modified reference areas Na, Nb, Nc and Nd. When agraphic representation similar to that of FIG. 8 is used, each of themodified reference areas thus resulting from the basic reference area N'shown in FIG. 7 can be represented by an area obtained by adding anincremental step or a decremental step to the basic reference area Ralong the line f in respect of predetermined ranges of angle of rotationof the matrix array 94 from the initial line OX (FIG. 7) depending uponthe direction in which the modified reference area is displaced from thebasic reference area N'. In this instance, each of the areas over whichthe detected image sensing zone M' is overlapped by the individualmodified reference areas resulting from the basic reference area N' canbe represented by the number of the logic "1" signals obtained by addingor subtracting a predetermined number to or from the number of the logic"1" signals represented by the portion Hf of the detected image sensingzone H shown in FIG. 8 in respect of predetermined ranges of angle ofrotation of the matrix array 94 depending upon the direction in whichthe modified reference area is displaced from the basic reference areaN' shown in FIG. 7.

FIG. 9 shows examples of the programs in accordance with which the fourmodified versions of the basic reference area R illustrated in FIG. 8are to be obtained on the basis of the above described principle. InFIG. 9, the modified reference areas area R in the graphicrepresentation of FIG. 8 are denoted by Ra, Rb, Rc and Rd in graphs (a),(b), (c) and (d), respectively. The modified reference areas Ra, Rb, Rcand Rd are assumed to correspond to the first, second, third and fourthmodified reference areas Na, Nb, Nc and Nd, respectively, shown in FIG.4 and are thus obtained when the basic reference area N' shown in FIG. 7is displaced forwardly, rearwardly, rightwardly and leftwardly in FIG.7. Thus, the modified reference area Ra obtained when the basicreference area N' is displaced forwardly in FIG. 7 is represented by anarea formed by subtracting a predetermined number q from the number p ofthe logic "1" signals produced at each of the predetermined angularintervals of 10 degrees in the vicinity of 90 degrees from the initialOX (FIG. 7) and adding the predetermined number q to the number p of thelogic "1" signals produced at each of the predetermined angularintervals of 10 degrees in the vicinity of 270 degrees from the initialline OX, as indicated in graph (a). Likewise, the modified referencearea Rb resulting from the displacement of the basic reference area N'in the rearward direction in FIG. 7 is represented by an area obtainedby adding the predetermined number q to the number p of the logic "1"signals produced at each of the predetermined angular intervals of 10degrees in the vicinity of 90 degrees from the initial line OX andsubtracting the predetermined number q from the number p of the logic"1" signals produced at each of the predetermined angular intervals of10 degrees in the vicinity of 270 degrees from the initial line OX, asindicated in graph (b). On the other hand, the modified reference areaRc resulting from the displacement of the basic reference area N' in therightward direction in FIG. 7 is represented by an area which isobtained by adding the predetermined number q to the number p of thelogic "1" signals produced at each of the predetermined angularintervals of 10 degrees in the vicinity of the initial line OX andsubtracting the predetermined number q from the number p of the logic"1" output signals produced at each of the predetermined angularintervals of 10 degrees in the vicinity of 180 degrees from the initialline OX, as indicated in graph (c). Conversely, the modified referencearea Rd resulting from the displacement of the basic reference area N'in the leftward direction in FIG. 7 is represented by an area obtainedby subtracting the predetermined number q from the number p of the logic"1" signals produced at each of the predetermined angular intervals of10 degrees in the vicinity of the initial line OX and adding thepredetermined number q to the number p of the logic "1" signals producedat each of the predetermined angular intervals of 10 degrees in thevicinity of 180 degrees from the initial line OX. Each of the angularranges over which the number p of the logic "1" signals produced at eachof the predetermined angular intervals is to be increased or decreasedby the predetermined number q in the above described fashion is assumed,by way of example, to be 90 degrees across each of 0, 90, 180 and 270degrees from the initial line OX.

The four modified reference areas Ra, Rb, Rc and Rd thus formulatedgraphically are respectively registered in four different memory units(not shown) in terms of the denotations respectively allocated to theindividual photoelectric transducer elements 96 of the matrix array 94and the individual angular intervals of the rotation of the matrix array94 from the initial line OX shown in FIG. 7. Each of such memory unitsmay comprise a predetermined number of memory cells respectivelyallocated to all the possible combinations of the above mentionedangular intervals and the respective denotations of the transducerelements 94 and may be electrically connected to memory readout meansoperative to deliver address signals to the memory cells allocated toeach of the angular intervals at each of the aforesaid time intervals.The memory units to be used for this purpose are essentially similar ineffect to the memory units 48a, 48b, 48c and 48d constituting the memorycircuit 48 shown in FIG. 5 and, for this reason, may be assumed to beconstituted by these memory units 48a, 48b, 48c and 48d, respectively.

As the linear-configuration matrix array 94 is rotated about the axis ofrotation O thereof, the memory cells constituting each of the memoryunits 48a to 48d are sequentially sampled by suitable address signalswhich are produced in synchronism with the individual angular intervalsof 10 degrees of rotation of the matrix array 94. Each of the memoryunits 48a to 48d is thus caused to produce a logic "1" output signalwhen the memory cell sampled by such an address signal falls within themodified reference area Ra, Rb, Rc or Rd registered in the particularmemory unit. The logic "1" output signals thus delivered from theindividual memory units 48a to 48d are fed to two-input logic "AND" gatecircuits forming part of an overlap area monitor circuit similar ineffect to the overlap area monitor circuit 42 shown in FIG. 5. Whenincorporated into the embodiment using the linear-configuration matrixarray 94, the overlap area monitor circuit 42 is arranged so that oneinput terminal of each of the logic "AND" gate circuits 60a to 60d isconnected to the respectively associated one of the memory units 48a to48d and the other input terminals of the "AND" gate circuits 60a to 60dare jointly connected to the individual photoelectric transducerelements 96 (FIG. 7) of the matrix array 94. When, thus, the matrixarray 94 is moving over a portion of the pattern on the drawing, each ofthe logic "AND" gate circuits 60a to 60d is supplied with a series oflogic "1" signals from those transducer elements 96 of the matrix array94 which fall within the detected image sensing zone M' shown in FIG. 7.Each of the logic "AND" gate circuits 60a to 60d is therefore operativeto produce a logic "1" output signal each time the memory cell sampledin the respectively associated one of the memory units 48a to 48d fallswithin the modified reference area Ra, Rb, Rc or Rd registered in thememory unit and in addition the photoelectric transducer element 96corresponding to the particular memory cell falls within the detectedimage sensing zone M' shown in FIG. 7. The logic "1" output signals thusproduced by the logic "AND" gate circuits 60a to 60d are supplied todigital counter circuits similar in effect to the counter circuits 64ato 64d of the overlap area monitor circuit 42 shown in FIG. 5. Each ofthe counter circuits 64a to 64d is clocked in synchronism with the clockfrequency at which the transducer elements 96 of the matrix array 94 aresequentially clocked and is thus operative to count the logic " 1"output signals from the associated "AND" gate circuit 60a, 60b, 60c or60d as the transducer elements 96 are clocked and the memory cells inthe associated memory unit 48a, 48b, 48c or 48d are sampled. At the endof the full turn of the matrix array 94 about the axis of rotation Othereof, an end-of-frame signal is supplied to each of the countercircuits 64a to 64d and causes each counter circuit to produce an outputsignal representative of the number of the logic "1" signals counted bythe counter circuit. The respective output signals produced by thecounter circuits 64a to 64b are supplied to a suitable centralprocessing unit (not shown) which may be preferably constructed andarranged in such a manner as to conduct the steps represented by theflowchart of FIG. 6. It will be apparent that each of the output signalsthus delivered from the counter circuits 64a to 64d in the abovedescribed fashion is representative of the area over which the hatchedarea H shown in FIG. 8 and representative of the detected image sensingzone M' shown in FIG. 7 is overlapped by each of the modified referenceareas Ra, Rb, Rc and Rd shown in the graphs (a), (b), (c) and (d),respectively, of FIG. 9. In FIG. 10, the overlap area between thedetected image sensing zone H and the modified reference area Rcresulting from the displacement of the basic reference area N' (FIG. 7)is displaced in the rightward direction is indicated by a cross-hatchedarea Hfc. In the graph of FIG. 10, the angles θ₁, θ₂, θ₃, θ₄ and θ₅ areassumed to be 150°, 180°, 210°, 240° and 270°, respectively, from theinitial line OX in FIG. 7.

The numbers p and q to determine the modified reference areas Ra to Rdto be registered in the memory units 48a to 48d, respectively, can bevaried from the central processing unit depending upon the desired widthof the cut to be made and/or the width of the pattern to be traced.

While it has been assumed that each of the described embodiment of thesystem according to the present invention is used in combination with anoxyacetylene cutting torch, the pattern tracing system herein proposedis compatible with a cutting machine using any other cutting tool suchas a rotary blade or may be incorporated into any of machines andequipment in which the tracing of a given pattern is required.Furthermore, the pattern to be traced by the system acccording to thepresent invention is not limited to a line drawn on a sheet of paper butmay be any geometrical or graphic pattern drawn or otherwise occurringon a uniplanar surface of any material insofar as the pattern ismonochromatically contrastive to the environment on the pattern-carryingsurface of the material.

While, furthermore, the image sensing unit of each of the embodimentshereinbefore described has been assumed to be responsive to the lightreflected from the front face of a drawing, it will be apparent that thesystem according to the present invention may be used in such a mannerthat the image sensing unit is responsive to the light passed throughthe material carrying the pattern to be traced, provided thepattern-carrying material is transparent or transluscent. The materialcarrying the pattern to be traced by the light reflected from or passedthrough the material may be positioned on any plane angled with respectto a horizontal plane if the image sensing unit is arranged to bemovable on a plane parallel with the plane on which the pattern-carryingmaterial is placed.

If the material carrying the pattern to be traced is placed on a movabletable, the system according to the present invention may be arranged sothat the image sensing unit is held stationary and the movable tablecarrying the pattern-carrying material thereon is driven to move withrespect to the image sensing unit in response to the signals suppliedfrom the central processing unit forming part of the tracing system.

While, furthermore, it has been described that the signals to dictatethe directions in which the image sensing unit is to be moved areproduced on the basis of the four modified reference areas formed infour different directions perpendicularly intersecting each other, suchsignals may be produced on the basis of the modified reference areasformed in more than four different directions equiangularly intersectingeach other so as to achieve higher accuracy in duplicating the patternto be traced.

Only two preferred embodiments of the pattern tracing system accordingto the present invention have been described hereinbefore but it will beapparent that such embodiments are merely illustrative of the essentialgist of the present invention and are subject to modification and chageif desired.

What is claimed is:
 1. A method of tracing a monochromaticallycontrasting pattern on a uniplanar surface, comprisingphotoelectricallyscanning at least a portion of the pattern on said uniplanar surface forproducing signals forming on a plane substantially parallel with saiduniplanar surface a detected image sensing zone substantially similar inconfiguration to said portion of the pattern on said uniplanar surface,registering pieces of information representative of a predeterminednumber of modified reference areas each displaced a predetermineddistance in a predetermined direction from a prescribed basic area onsaid plane, sampling said pieces of information for delivering signalsrepresentative of each of the individual modified reference areas,producing in responsive to the signals representative of said detectedimage sensing zone and the signals representative of each of saidmodified reference areas a signal representative of the overlap areaover which the detected image sensing zone is overlapped by each of themodified reference area, selecting from among the individual signalsrespectively representative of the overlap areas between said detectedimage sensing zone and said modified reference areas a signalrepresentative of an overlap area satisfying predetermined conditions,producing a control signal representative of the predetermined directionallocated to the modified reference area corresponding to the signalselected, and photoelectrically scanning another portion of the patternon said uniplanar surface depending upon said control signal.
 2. Amethod as set forth in claim 1, in which said pattern on said uniplanarsurface is scanned by the use of an area-configuration matrix arraymovable on said plane and comprising a predetermined number of rows eachconsisting of a predetermined number of photoelectric transducerelements arranged linearly, said pattern being scanned by selecting saidrows in a predetermined sequence and sequentially sampling theindividual transducer elements of the selected row at a predeterminedfrequency, said matrix array being moved in the direction represented bysaid control signal.
 3. A method as set forth in claim 2, in which thepieces of information representative of each of said modified referenceareas are stored in a memory unit comprising a predetermined number ofmemory cells respectively allocated to said transducer elements of saidmatrix array, said memory cells being sequentially sampled at afrequency substantially synchronized with said predetermined frequencyfor producing said signals representative of said modified referenceareas.
 4. A method as set forth in claim 1, in which said pattern onsaid uniplanar surface is scanned by the use of a linear-configurationmatrix array which is rotatable about an axis substantially normal tosaid plane and which comprises a predetermined number of photoelectrictransducer elements arranged linearly between the innermost andoutermost ends of the matrix array and having respective denotations interms of their respective distances from said axis, said photoelectrictransducer elements being sampled at each of predetermined angularintervals about the axis of rotation of the matrix array.
 5. A method asset forth in claim 4, in which the pieces of information representativeof each of said modified reference areas are stored in a memory unitcomprising memory cells respectively allocated to all the possiblecombinations of said angular intervals and the respective denotations ofsaid transducer elements, said memory cells being sampled at each oftime intervals respectively corresponding to said predetermined angularintervals, said matrix array being moved in the direction respresentedby said control signal.
 6. A method as set forth in claim 2 or 3, inwhich said matrix array is movable in substantially perpendicularlycrossing four different directions on said plane and in which thepredetermined directions in which said modified reference areas arerespectively displaced from said basic reference area correspond to saidfour different directions, respectively.
 7. A method as set forth inclaim 4 or 5, in which the axis of rotation of said matrix array ismovable in substantially perpendicularly crossing four differentdirections on said plane and in which the predetermined directions inwhich said modified reference areas are respectively displaced from saidbasic reference area correspond to said four different directions,respectively.
 8. A method as set forth in any one of claims 1 to 5, inwhich the signal representative of each of said overlap areas isproduced by producing a predetermined binary signal in the presence ofboth of the signal falling within said detected image sensing zone andthe signal falling within each of said modified reference areas andcounting the resultant binary signals.
 9. A method as set forth in anyone of claims 1 to 5, in which the signal representative of the overlaparea satisfying said predetermined conditions is selected by a processcomprising a first step of registering the signals respectivelyrepresentative of said overlap areas, a second step of determiningwhether or not all the overlap areas respectively represented by thesignals registered in the first step are zeros, a third step ofproducing a signal if the answer in the second step is in theaffirmative, a fourth step of excluding from the signals registered inthe first step a signal representative of the overlap area correspondingto the modified reference area displaced from said basic reference areain a direction corresponding to the direction represented by the controlsignal produced in an immediately preceding cycle of operation if theanswer in the second step is in the negative, a fifth step ofdetermining whether or not only one of the overlap areas respectivelyrepresented by the signals remaining in said fourth step is closer to apredetermined value than the overlap areas respectively represented bythe others of the remaining signals, a sixth step of producing as thefirst named control signal a signal representative of the predetermineddirection in which the modified reference area corresponding to saidonly one of the overlap areas if the answer in the fifth step is in theaffirmative, a seventh step of producing as the first named controlsignal a signal representative of the direction represented by thecontrol signal produced in the immediately preceding cycle of operationif the answer in the fifth step is in the negative, and an eighth stepof registering the signal produced in the sixth or seventh step.
 10. Aphotoelectric pattern tracing system for tracing a monochromaticallycontrasting pattern on a uniplanar surface, comprisingan image sensingunit which is movable on a plane substantially parallel with saiduniplanar surface and which is photoelectrically responsive to thepattern on the uniplanar surface, a predetermined number of memory unitseach having stored therein pieces of information representative of amodified reference area displaced a predetermined distance in apredetermined direction from a prescribed basic reference area on saidplane, image readout means operative to electrically scan said imagesensing unit for causing the image sensing unit to deliver signals inresponse to at least a portion of said pattern, said signals forming onsaid plane a detected image sensing zone substantially similar inconfiguration to said portion of said pattern, memory readout meansoperative to sample the pieces of information stored in each of saidmemory units for causing the individual memory units to deliver signalsrepresentative of the modified reference areas respectively allocated tothe memory units, an overlap area monitor circuit responsive to thesignals delivered from said image sensing unit and said memory units andoperative to produce a signal representative of the overlap area overwhich the basic reference area represented by the signals delivered fromthe image sensing unit is overlapped by the modified reference arearepresented by the signals delivered from each of said memory units,computing means responsive to the signals from said overlap area monitorcircuit and operative to select from among the signals produced by theoverlap area monitor circuit a signal representative of an overlap areasatisfying predetermined conditions and to produce an output signalrepresentative of the predetermined direction allocated to the memoryunit from which the signals resulting in the signal selected by thecomputing means are delivered, and drive means responsive to the outputsignal from the computing means and operative to drive said imagesensing unit to move a predetermined distance on said plane in thedirection represented by the output signal from the computing means. 11.A photoelectric pattern tracing system as set forth in claim 10, inwhich said image sensing unit comprises an area-configuration matrixarray comprising a predetermined number of rows each consisting of apredetermined number of photoelectric transducer elements arrangedlinearly and in which said image readout means is electrically connectedto the transducer elements of all the rows and is operative to selectthe rows in a predetermined sequence and to sequentially sample theindividual transducer elements of the selected row at a predeterminedfrequency.
 12. A photoelectric pattern tracing system as set forth inclaim 11, in which each of said memory units comprises a predeterminednumber of memory cells respectively allocated to the transducer elementsof said image sensing unit and in which said memory readout means iselectrically connected between said image readout means and each of saidmemory units and is operative to deliver a succession of address signalsto said memory cells, respectively, of each of the memory units at afrequency substantially synchronized with said predetermined frequency.13. A photoelectric pattern tracing system as set forth in claim 10, inwhich said image sensing unit comprises a linear-configuration rotarymatrix array which is rotatable about an axis substantially normal tosaid plane and which comprises a predetermined number of photoelectrictransducer elements arranged linearly between the innermost andoutermost end of the matrix array and having respective denotations interms of their respective distances from said axis, said image readoutmeans being electrically connected to said transducer elements and beingoperative to sample the individual transducer elements at each ofpredetermined angular intervals about said axis.
 14. A photoelectricpattern tracing system as set forth in claim 13, in which each of saidmemory units comprises a predetermined number of memory cellsrespectively allocated to all the possible combinations of said angularintervals and the respective denotations of said transducer elements andin which said memory readout means is electrically connected betweensaid image readout means and each of said memory units and is operativeto deliver address signals to the memory cells allocated to each of saidangular intervals at each of said time intervals.
 15. A photoelectricpattern tracing system as set forth in any one of claims 10 to 12, inwhich said image sensing unit is movable in substantiallyperpendicularly crossing four different directions on said plane and inwhich the predetermined directions in which said modified referenceareas are resprectively displaced from said basic reference areacorrespond to said four different direction, respectively.
 16. Acombination of a photoelectric pattern tracing system as set forth inclaim 15 and a machine tool including at least one machining membermechanically connected to and movable with said image sensing unit. 17.A photoelectric pattern tracing system as set forth in claim 13 or 14,in which the axis of rotation of said matrix array is movable insubstantially perpendiculary crossing four different directions on saidplane and in which the predetermined directions in which said modifiedreference areas are respectively displaced from said basic referencearea correspond to said four different directions, respectively.
 18. Aphotoelectric pattern tracing system as set forth in any one of claims10 to 14, in which said overlap area monitor circuit comprises logicgate circuits electrically connected jointly to said image sensing unitand respectively to said memory units and each operative to produce apredetermined binary signal in the presence of both of the signaldelivered from the image sensing unit and the signal delivered form therespectively associated one of the memory units, and resettable countercircuits respectively connected to said logic gate circuits and eachoperative to count the binary signals delivered from the respectivelyassociated one of the logic gate circuits, said counter circuits beingjointly connected to said image readout means for being reset each timeall the transducer elements of the image sensing unit are sampled.
 19. Acombination of a photoelectric pattern tracing system as set forth inclaim 18 and a machine tool including at least one machine toolmechanically connected to and movable with said image sensing unit. 20.A photoelectric pattern tracing system as set forth in any one of claims10 to 14, in which said computing means comprises first means forregistering the signals delivered from said overlap area monitor circuitand respectively representative of the overlap areas over which saiddetected image sensing unit is overlapped by the modified referenceareas respectively allocated to said memory units, second means fordetermining whether or not all the overlap areas respectivelyrepresented by the signals registered in said first means are zeros,third means responsive to the positive answer in the second means,fourth means responsive to the negative answer in the second means andoperative to exclude from the signals registered in said first means thesignal representative of the overlap area over which said detected imagesensing zone is overlapped by the modified reference area displaced fromsaid basic reference area in the direction corresponding to thedirection in which said image sensing unit is moved in an immediatelypreceding cycle of operation, fifth means for determining whether or notonly one of the overlap areas respectively represented by the signalsremaining in said fourth means is closer to a predetermined value thanthe overlap areas respectively represented by the others of theremaining signals, sixth means responsive to the affirmative answer inthe fifth means for producing a signal representative of thepredetermined direction allocated to the memory unit from which thesignals resulting in the signal representative of said only one of theoverlap areas are delivered, seventh means responsive to the negativeanswer in said fifth means for producing a signal representative of thedirection in which said image sensing unit is moved in said immediatelypreceding cycle of operation, the signal delivered from either of saidsixth and seventh means being fed to said drive means, and eighth meansfor registering therein and in said fourth means the signal deliveredfrom the sixth or seventh means.
 21. A combination of a photoelectricpattern tracing system as set forth in claim 20 and a machine toolincluding at least one machining member mechanically connected to andmovable with said image sensing unit.
 22. A combination of aphotoelectric pattern tracing system as set forth in any one of claims10 to 14 and a machine tool including at least one machining membermechanically connected to and movable with said image sensing unit. 23.A combination as set forth in claim 22, in which said machining memberis constituted by an oxyacetylene cutting torch.
 24. A combination asset forth in claim 22, in which said machining member is constituted bya rotary cutting blade rotatable about an axis movable with said imagesensing unit.